1. Field of the Invention
The present invention relates to techniques for easily writing pieces of software into a rewritable and nonvolatile memory with which an in-vehicle computer is integrated.
2. Description of the Related Art
Electronic control units (ECUs) installing therein a microcomputer have been widely used for vehicle control in various ways. In vehicles in which such an ECU is installed beforehand, the microcomputer is operative to execute vehicle control in accordance with software stored in advance in a memory. In such a software controlled vehicle, a nonvolatile memory is used to store therein a piece of software that corresponds to the type of the software-controlled vehicle. This allows ECUs to accept various types of vehicles without changing the hardware structures of the ECUs.
Particularly, different types, such as different grades, of automobiles respectively install therein corresponding different types of ECUs. Moreover, there are various types of ECUs at least one of which a user optionally can select to thereby install the selected ECU in a user's own automobile. In addition, default values in a map (data table), which is used to control the engine, stored in advance in a memory of an ECU installed in a vehicle must be rewritten into values corresponding to the type of the vehicle.
These circumstances set force above have advances the adoption of an electrically rewritable memory for storing a piece of software.
The adoption of electrically rewritable memory allows a piece of software corresponding to the type of a vehicle to be written in the electrically rewritable memory at vehicle production lines and/or service centers for maintenance of vehicle. This permits ECUs to meet various types of vehicles. It is to be noted that ECUs with a microcomputer integrated with an electrically rewritable and nonvolatile memory have been well known.
An example of ways for changing vehicle control design is disclosed in Japanese Unexamined Patent Publication No. H05-38969.
In one typical example disclosed in the Patent Publication, a memory card is prepared as an example of removable external storage devices for microcomputers, and a piece of software created based on new vehicle design concept is written into the prepared memory card.
Next, the memory card is inserted into a card slot of the microcomputer. The microcomputer is programmed to load the piece of software stored in the memory card into a RAM of the microcomputer, making it possible to freely change the design of vehicle control to be executed by an ECU.
An ECU, which is disclosed in the Patent Publication and designed to load a piece of software from a RAM of the microcomputer to thereby execute vehicle control, has an advantage capable of easily using a removable external memory device. This makes it easy to change and/or update the piece of software installed in the ECU. The RAM however loses the piece of software stored therein when power to be supplied to the RAM is switched off. For this reason, during boot-up, the ECU (microcomputer) disclosed in the Patent Publication need load the piece of software stored in an external storage device, which may take a lot of time to boot up the ECU (microcomputer).
On the other hand, an ECU integrated with electrically rewritable and nonvolatile memory need not load a piece of software stored in an external storage device during boot-up, which makes it possible to boot up the ECU at high speed.
In rewriting of a piece of software stored in the electrically rewritable and nonvolatile memory, however, a tool designed specifically for the rewriting of the piece of software stored in the electrically rewritable and nonvolatile memory is required. This may make it difficult to easily rewrite a piece of software stored in the electrically rewritable and nonvolatile memory.
Specifically, if an ECU with an electrically rewritable and nonvolatile memory is installed in a vehicle, in order to easily rewrite a piece of software stored in the electrically rewritable and nonvolatile memory of the ECU, various pieces of software corresponding to a plurality of types of vehicles and the tool designed specifically for the software rewriting need be provided at each of service centers. This may increase the cost required to improve the level of convenience in rewriting of a piece of software stored in the electrically rewritable and nonvolatile memory.
In addition, when an ECU with an electrically rewritable and nonvolatile memory is installed in a vehicle, volatilization of a part of a piece of software stored in the electrically rewritable and nonvolatile memory may take a lot of time to repair the ECU (vehicle). This is because no pieces of software are prepared at each of service centers, auto-repair shops, and other similar shops.